1. Field of the Invention
The present invention relates to syringes and more particularly concerns disposable syringes having single-use and medication saving features.
2. Background
In the United States and throughout the world the multiple use of hypodermic syringe products which are intended for single use only is instrumental in drug abuse and in the transfer of contagious diseases. Intravenous drug users who routinely share and re-use syringes are a high risk group with respect to the AIDS virus. Also, the effects of multiple use are a major concern in some countries where repeated use of syringe products during mass inoculation programs may be responsible for the spread of many diseases. Re-use of single use hypodermic syringe assemblies is also instrumental in the spread of drug abuse even in the absence of infection or disease.
Many attempts have been made to remedy this problem. Most notable are early contributions which relied on a specific act to destroy the syringe after use either by using a destructive device or providing a syringe assembly with frangible zones so that the syringe could be rendered inoperable by the application of force. Other attempts involve the inclusion of structure which would allow the destruction or defeating of the syringe function through a conscious act by the syringe user. Although many of these devices work quite well they do require the specific intent of the user followed by the actual act to destroy or render the syringe inoperable. These devices are not effective with a user having the specific intent to re-use the hypodermic syringe. Accordingly, there is a need for a single use hypodermic syringe which becomes inoperative or incapable of further use automatically without any additional act on the part of the user. This automatic function is much harder to provide because the means for rendering the syringe inoperable must not prevent its filling or use under normal conditions.
In single-use syringes using needle assemblies having a hub attached to a needle cannula there is a need to prevent the removal of the needle assembly after the use of the single-use syringe so that the needle assembly cannot be used again with other syringes.
There is also a need in single-use syringes to minimize or eliminate wasted medication in the injection process. This is especially true in mass inoculation programs involving large numbers of people and in many cases limited financial resources. Medication which is not delivered, because it is trapped in the interior of the syringe tip after the plunger reaches its maximum distal displacement, can prove costly. Even with a small number of injections, an entire dose may be lost through medication which is trapped in the syringe and not delivered.